Method and apparatus for casting permanent magnets



Sept. 16, 1941. J, s v 2,256,218

METHOD AND APPARATUS FOR CASTING PERMANENT MAGNETS Filed 001;. 4;, 1939 Inventor: John byseaver,

His Attorney.

Patented Sept. 16, 1941 METHOD AND APPARATUS FOR CASTING PERMANENT MAGNETS John 'D. Seaver, Cohasset, Mass., assignor to General Electric Company, a corporation of New York Application October 4, 1939, Serial No. 297,910

Claims.

The present invention relates to a method for casting permanent magnets and particularly to' a method for casting magnets which are adapted for use in watt hour meters and like devices.

It 'is one of the objects of the present invention to provide a method and apparatus for simultaneously casting a plurality of pieces'of permanent magnet alloys onto a metal base plate. A further object of the invention is to provide a method for casting economically small permanent magnets. Other objects will appear hereinafter. The novel features which are characteristic of my invention are set forth with particularity in the appended claims. however will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 is a plan view of a multiple mold and rotating casing therefor; Fig. 2 is a cross sectional view of the mold and casing illustrated in Fig. 1 when tilted to receive molten metal; Fig. 3 is a perspective view of one of the sand indicated at 9. The upper ends of the projections 8 are slightly mushroomed, as indicated at H).

My invention itself molds illustrated in Fig. 1 and a base plate for closing the openings inthe mold and onto which the magnetic material is cast; Fig. 4 is a cross sectional view of the assembled sand mold and closure plate; Fig. 5 is a perspective view of a casting as removed from a mold; while Fig. 6 is a view in elevation of a trimmed casting and base plate as assembled in a meter yoke or shield.

In carrying out my invention I employ apermanent magnet alloy composition which has a very high coercive force, for example a magnet alloy of the well known alnico type which may consist of iron, nickel and aluminum or these elements in combination with others, for example cobalt, copper, titanium etc. The alloy preferably is a cast alloy and in fabricating it I employ a sand mold which, if desired, may consist of a plurality of similar molds as indicated at l on the drawing. Each mold has an upper opening 2 and a lower opening 3 which corresponds to the shape of the magnet polepieces 4 and 5 to be cast therein. In thefabrication of permanent magnets suitable for use in watt hour meters and the like, it maybe desirable to employ a soft iron base plate 6 which serves to support polepieces 5 and .5 and also to form a continuation of the steel yoke or shield I. If desired however the base plate 6 may be formed of any In the casting operation the sand molds l are circumferentially arranged in a container H which is provided with an elevated platform I 2 which supports the forward ends of the various molds l as indicated in Fig. 2. The container II is driven from a source of power, not shown, through a shaft I3 and it may be tilted from a horizontal position as indicated in Fig. 2. The container fl is rotated at a desired speed and the metal alloy poured into the various openings 2 and 3 of the molds. The rotation of the molds forces the molten metal against the base plate 6 and around projections 8 so that polepieces 4 and 5 when cooled, are firmly attached thereto. When the necessary amount of molten metal has been poured into the molds and the metal has solidified to the desired extent the castings may be removed and the sprues H cut ofi and the upper surface of each polepiece ground to the desired. extent after which it may be mounted in a meter structure or yoke I as indicated in Fig. 6.

My improved casting process and apparatus is particularly well adapted for the production of small permanent castings of the alnico type. Such castings may be made by my process with very short sprues which results in certain economies since the sprues are short enough to permit re-melting. If the castings were made with long sprues re-melting of such sprues might not be satisfactory because of difiiculty in controlling the aluminum content of the resulting alloy. The grain structure of the resulting alnico type castings is very fine due to the churning and violent turbulence of the metal as it fills the molds and solidifies.

The fine grain results in an alloy of considerable strength which may be ground far more easily than castings made by the usual gravity process. Although fine grain castings may be suitable material for example chrome steel or even non-magnetic metal. To secure a firm connection between the individual polepieces of the base plate, the latter is provided with projections 8 which are punched out of the iron as obtained in a limited way by pouring gravity castings close to the freezing temperature of the metal, in my improved process for making permanent magnets of the alnico type close control of pouring temperature is not necessary since the metal may be poured at a higher temperatime than that employed for making gravity castings.

The cast metal may be cooled in the mold if desiredfand at a rate which will effect a condition of precipitation and the desired magnetic characteristics. in the alloy. If desired, however,

the alloy ma be reheated at a temperature below the melting point to assure complete precipitation. Although I have illustrated my invention with a plurality of sand molds I, it is obvious that a single multiple cavity mold could be employed if desired.

What I claim as new and desire to secure by Letters Patent or the United States,'is:

- 1. A process for casting permanent magnet al-- 2. A process for casting permanent magnetalloys which comprises rotating a mold having openings therethrough and a metal plate closing the outer ends of said openings, said plate having a projection thereon, pouring molten metal into said mold and around said projection to thereby simultaneously form a pair of polepieces mounted on said plate.

said closure plates.

.3. A mold having a plurality of openings therethrough and a metal plate closing said openings and onto which molten metal may be poured.

4. A mold having an upper and a lower opening extending therethrough and a metal plate closing said openings, said plate having a plurality of projections thereon extending into said openings and onto which the molten metal may be poured.

5. A centrifugal casting machine which comprises a supporting member, a multiple cavity mold arranged on said member, said mold having a plurality of pairs of circumferentially arranged openings extending therethrough, each pair of openings comprising an upper and a lower opening, a plurality of spaced metal plates, each plate closing the outer ends of a pair of. said openings, means for rotating said supporting member, and means whereby molten metal may be poured directly into the openings in said mold and onto JOHN D; SEAVER. 

